This invention relates to a method of downlink operation in a communication system.
In Release 6 universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN) frequency division duplex (FDD) systems a terminal can be in one of two states in the downlink, cell forward access channel (Cell_FACH) or cell dedicated channel (Cell_DCH). In Cell_FACH, there is no active connection to the Node B at the physical layer, no regular power control, or uplink. In Cell_DCH, there is continuous power control and active uplink and downlink. However, it is not desirable to keep the terminal in Cell_DCH state, as this uses up resources, so it is usual to move the terminal to another state when not actually communicating. Although it is not generally efficient to do so, the Cell_FACH state can be used for transmissions of small amounts of data. There are discussions to increase throughput and reduce latency requirements for users in Cell_FACH state by enabling the NodeB to map the data of the forward access channel (FACH) on high speed physical downlink shared channel (HS-PDSCH).
One proposal under discussion in 3rd generation partnership project (3GPP) is that the high speed downlink shared channel (HS-DSCH) be used for carrying the FACH for users in CELL_FACH state, rather than using the secondary common control physical channel (S-CCPCH). This proposal is based on the assumption that the HS-DSCH would be transmitted on several consecutive occasions to the terminal, or user equipment (UE) to overcome the problems of feedback free operation and ensure correct reception at the same time. The high speed shared control channel (HS-SCCH) is required to indicate the start of the HS-DSCH transmission. Although consecutive transmission has advantages concerning latency, overcoming the problems due to different knowledge states in different involved entities, when comparing high speed downlink packet access (HSPDA) transmission versus S-CCPCH transmission as currently used as a physical channel for carrying the FACH, is not considered here.
Conventionally, the S-CCPCH, under control of the radio network controller (RNC) and the NodeB, the NodeB being used as transmitter only, has been used to carry the FACH and so the mobility procedures were controlled by the RNC. To enable inter-frequency and inter-radio access technology (RAT) measurements, FACH measurement occasions were assigned to different UEs, depending on a modulo cell radio network temporary identifier (C-RNTI) operation. In Cell-FACH state, a UE is requested to listen continuously whether it is scheduled, or not. For inter-frequency or inter-RAT measurements the UE needs to listen to other frequencies, so the FACH measurement occasions were introduced. The other measurements for handover are done based on the UE's internal identifier and when the RNC recognises this, the UE is switched to another frequency to do its measurements. However, the Node B has no knowledge of the measurement occasions as the Node B schedules as directed by the RNC. If the Node B is scheduling on HS-DSCH without knowing the measurement occasions, the Node B may try scheduling when the UE is on another frequency. This can give rise to loss of repeat transmissions due to the length of time that the UE is off the scheduling frequency.